investigation on an innovative method for high-speed low

materials

Article

Investigation on an Innovative Method forHigh-Speed Low-Damage Micro-Cutting of CFRPComposites with Diamond Dicing Blades

Zewei Yuan 1,*, Jintao Hu 1, Quan Wen 2, Kai Cheng 3 and Peng Zheng 1

1 School of Mechanical Engineering, Shenyang University of Technology, Shenyang 110870, China;[email protected] (J.H.); [email protected] (P.Z.)

2 School of Mechanical engineering, Northeastern University, Shenyang 110819, China;[email protected]

3 College of Engineering, Design and Physical Sciences, Brunel University London, London UB8 3PH, UK;[email protected]

* Correspondence: [email protected]

Received: 7 September 2018; Accepted: 11 October 2018; Published: 13 October 2018��

Abstract: This paper presents an innovative method for high-speed micro-cutting of carbon fiberreinforced plastics (CFRP). It employs a diamond dicing blade for micromachining applications,with a thickness of about 200 µm and rotational speeds up to 30,000 rpm so as to meet the low-damagesurface integrity requirements. The process parameters, cutting damage, surface roughness, and thespindle vibration were thoroughly investigated to evaluate and validate the method. The resultsindicate that a high cutting speed up to 76 m/s not only remarkably increases the rigidity of anultra-thin dicing blade, but also decreases the cutting depth per diamond grit to below 10 nm,both of which are very conducive to obtaining a very fine machined surface of about Ra 0.025 µm,with no obvious damage, such as delamination, burrs, and fiber pull out. The serious spindlevibration limits the rotational speed to increase further, and the rotational speed of 25,000 rpmachieves the best fine machined surface. Furthermore, unlike most research results of the drillingand milling method, the proposed micro-cutting method obtains the maximum cutting currentand surface roughness when cutting at 0◦ fiber orientation, while obtaining a minimum cuttingcurrent and surface roughness when cutting at 90◦ fiber orientation. The metal-bonded dicing bladeachieves smaller surface roughness than the resin-bonded dicing blade. This paper also discusses thecutting mechanism by investigating the morphology of the machined surface and concludes that themicro breakage and plastic-flow in local regions of fibers and resin are the main material removalmechanisms for dicing CFRP composites with a diamond abrasive blade.

Keywords: CFRP composites; diamond dicing blades; micro cutting; low-damage surface;surface roughness

1. Introduction

Carbon fiber reinforced plastic (CFRP) composites, created by blending carbon fibers into plasticresin, have a variety of desirable properties including low density, high stiffness to weight ratio,excellent fatigue, corrosion and wear resistance, outstanding toughness and damage tolerance,high dimensional stability, excellent chemical resistance, and low friction coefficient, thermal expansion,and electrical conductivity, which cannot be obtained from conventional metals such as steel andaluminum [1–3]. Due to the combination of these significantly distinguished mechanical and thermalproperties, CFRP composites have been widely used in place of metals in many different applications,such as aerospace and commercial aircraft, marine, medical prosthesis, sports goods, robot arms,

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Materials 2018, 11, 1974 2 of 17

and racing cars [4,5]. In order to meet dimensional tolerance, surface quality, and other functionalrequirements in these application fields, secondary machining processes such as milling, drilling,grinding, trimming, and waterjet cutting are usually necessary to carry out during the manufacturing ofcomponents from CFRP composites [6–8]. However, CFRP composites are a typical difficult-to-machinematerial due to its heterogeneity, anisotropy of mechanical properties, and low thermal conductivity [9].It is difficult for traditional methods to machine CFRP composite with fine quality. During machining,very rapid cutting tool wear development is experienced [10]. Additionally, serious surface integritydamage is often produced in the machined CFRP parts, such as delamination, burrs, fiber pull out,fiber matrix debonding, and inadequate surface roughness of the cut walls, which will remarkablyreduce the mechanical performance of the CFRP parts [11–13].

Many researchers identified the type and orientation of fiber, cutting parameters, and toolgeometry as decisive factors for the cutting process [14,15]. They researched the cutting parametersincluding cutting speed and feed rate, the tool materials and geometry, fiber orientation angle,the cutting temperature, and cooling style to improve the machining quality of CFRP [6,16]. In addition,the evaluation of cutting force and hole quality, such as delamination and other damage, is oftenconducted [17,18]. Orthogonal cutting and macroscopic or microscopic numerical simulationsare effective methods to investigate the material removal mechanisms and fundamental failuremodes [19,20]. These investigations make significant improvement in reducing damage size suchas delamination, fiber pull out, and the surface roughness of the machined walls. For example,the sizes of delamination and burrs have been controlled in millimetric or submillimetric ranges.The surface roughness of the drilling or milling walls can be reduced to within the dimension of severalmicrometers. Even so, the machining quality cannot meet the requirements of CFRP composites inmany new applications such as automobiles, laptop computers, space shuttles, and satellites [21].These applications usually pursue submicrometer, or even better, cutting damage for CFRP composites.One of most important reasons to produce machining damage is rapid tool wear caused by abrasivesof CFRP composites, resulting in a decrease of tool cutting life and an increase of manufacturingcosts [22]. After the tool wears out, it is easy to generate vibration during the machining process,the cutting performance of the material is degraded, and the heat energy accumulation increasesduring the cutting process, so that the tool accelerates wear [23]. Therefore, diamond coated carbide,diamond abrasive, and polycrystalline diamond tools are usually employed to reach a sufficient toollifetime and to reduce the machining damage [24–26]. Many recent studies have demonstrated thatdiamond abrasive tools can generate a low-damage surface with average surface roughness of aboutRa 1.5 µm and higher dimensional accuracy [27,28]. Later, rotary ultrasonic machining produced evenbetter surface quality with a surface roughness of about Ra 1.0 µm [29–31]. Other research aboutthe machining of CFRP composites indicated that high-speed machining with spindle speeds up to60,000–80,000 rpm could also generate good machining surface and high machining efficiency, mainlydue to the remarkable reduction of cutting forces [32,33]. These studies proved that high-speed cuttingwith abrasive tools generates a better surface intensity for CFRP composites.

Besides conventional methods, non-conventional machining methods including water jet cutting,abrasive jet cutting, electrical discharge machining, and laser machining are common methods forcutting CFRP composites and other difficult-to-cut materials [34–36]. However, disadvantages ofwater jet cutting are the elaborate microfiltration before, and the treatment and disposal of water after,machining. As an alternative tool for the cutting of CFRP composites, laser cutting has non-contact,dry, and abrasionless advantages [37]. Its heat affected zone can be controlled in the dimension of10–200 µm, depending mainly on the intensity of the laser beam, the intensity profile, and the thicknessof laminates [38,39].

Diamond blades, created by embedding diamond particles in a metal matrix or brazing diamondparticle onto the borders of a steel core, can increase significantly the life of cutting tools, especiallyfor high-speed machining hard-to-cut materials. It was first widely designed to cut hard or abrasivematerials, such as concrete, marble, stone, and ceramics, when its thickness and the size of diamond

Materials 2018, 11, 1974 3 of 17

particles are large [40–42]. Then, ultra-thin and high-precision diamond blades are developed to use inslicing, dicing wafer, cut-off, singulation, grooving, slotting, cross sectioning, sample preparation, gangsawing, slabbing, and fine cutting applications. As one of the most common methods for precisioncutting, bladed dicing is characterized by using abrasive thin blades as the cutting element [43,44].The dicing blade is fixed on a high-speed spindle normally supported by aerostatic or ceramicbearings. The blade can reach up to 60,000 rpm and a blade with a diameter of 51 mm wouldreach a peripheral cutting speed at about 160 m/s. Thus, a high cutting speed and the well-wearingresistance of diamond abrasives are an effective way to reduce the machining damage of naturefiber composites and CFRP composites [45,46]. Therefore, diamond dicing blades are novel to use inthe micro cutting of CFRP composites, especially with micron-sized or submicron-sized machiningdamage and surface roughness.

To satisfy the high machining quality demands in new applications of automobiles, laptopcomputers, space shuttles, and satellites, this work proposed a new high-speed micro-cutting methodfor CFRP composites. It employed diamond abrasive dicing blades with a thickness of about200 µm to cut CFRP laminates with spindle speeds of up to 40,000 rpm. The cutting parameters,cutting damage, surface roughness, and the influence of spindle vibration were analyzed in detail.Additionally, the cutting mechanisms were also discussed with the help of a scratching experiment onthe UMT-TriboLab platform (Bruker, Madison, WI, USA).

2. Methodology and Experiments of Micro-Cutting CFRP Composites

Basically, the quality of kerf depends on the combination of the material being worked uponand the parameters of the cutting process, cooling system, feed speed, type of blade, and peripheralspeed [47]. However, for the ultraprecision dicing of CFRP composites, the failure mechanism ismore complex than hard and brittle materials because of its heterogeneity, anisotropy of mechanicalproperties, and low thermal conductivity. Therefore, the comprehensive factors that affect cuttingdamage should be investigated. As shown in Figure 1, the dicing machine has an accuracy as smallas 1 µm. A CFRP laminate was fixed on a ceramic sucker so that it undergoes uniform load when itis chucked.

Materials 2018, 11, x FOR PEER REVIEW 3 of 17

in slicing, dicing wafer, cut-off, singulation, grooving, slotting, cross sectioning, sample preparation,

gang sawing, slabbing, and fine cutting applications. As one of the most common methods for

precision cutting, bladed dicing is characterized by using abrasive thin blades as the cutting element

[43,44]. The dicing blade is fixed on a high-speed spindle normally supported by aerostatic or ceramic

bearings. The blade can reach up to 60,000 rpm and a blade with a diameter of 51 mm would reach a

peripheral cutting speed at about 160 m/s. Thus, a high cutting speed and the well-wearing resistance

of diamond abrasives are an effective way to reduce the machining damage of nature fiber composites

and CFRP composites [45,46]. Therefore, diamond dicing blades are novel to use in the micro cutting

of CFRP composites, especially with micron-sized or submicron-sized machining damage and

surface roughness.

To satisfy the high machining quality demands in new applications of automobiles, laptop

computers, space shuttles, and satellites, this work proposed a new high-speed micro-cutting method

for CFRP composites. It employed diamond abrasive dicing blades with a thickness of about 200 μm

to cut CFRP laminates with spindle speeds of up to 40,000 rpm. The cutting parameters, cutting

damage, surface roughness, and the influence of spindle vibration were analyzed in detail.

Additionally, the cutting mechanisms were also discussed with the help of a scratching experiment

on the UMT-TriboLab platform (Bruker, Madison, United States).

2. Methodology and Experiments of Micro-Cutting CFRP Composites

Basically, the quality of kerf depends on the combination of the material being worked upon and

the parameters of the cutting process, cooling system, feed speed, type of blade, and peripheral speed

[47]. However, for the ultraprecision dicing of CFRP composites, the failure mechanism is more

complex than hard and brittle materials because of its heterogeneity, anisotropy of mechanical

properties, and low thermal conductivity. Therefore, the comprehensive factors that affect cutting

damage should be investigated. As shown in Figure 1, the dicing machine has an accuracy as small

as 1 μm. A CFRP laminate was fixed on a ceramic sucker so that it undergoes uniform load when it

is chucked.

Figure 1. Slicing machine and its parameters. CFRP: carbon fiber reinforced plastic. Figure 1. Slicing machine and its parameters. CFRP: carbon fiber reinforced plastic.

As illustrated in Figure 2, the control and display system in the machine was used to locate andobserve the cutting kerf. It is easy to calculate the wear amount of the dicing blade by twice toolsetting before and after the dicing process. Due to the sensitivity of CFRP composites to machiningtemperature, the dicing blade and cutting region of the workpiece were cooled by the coolant systemduring the dicing process. Hereby, deionized water was used as coolant. Furthermore, the vibration ofthe spindle has an important influence on the micro-cutting damage of CFRP composites, so a vibrationdata acquisition system was fixed onto the dicing machine. Two vibration sensors were adhered onto

Materials 2018, 11, 1974 4 of 17

the surface of spindle with an angle of 90◦ to perceive the vertical and horizontal vibrations of thespindle. Because it is difficult to fix a dynamometer onto the cutting machine, the cutting current wasmeasured to reflect the variation of the cutting force.Materials 2018, 11, x FOR PEER REVIEW 4 of 17

Figure 2. Schematic diagram of dicing system for CFRP composites.

As illustrated in Figure 2, the control and display system in the machine was used to locate and

observe the cutting kerf. It is easy to calculate the wear amount of the dicing blade by twice tool

setting before and after the dicing process. Due to the sensitivity of CFRP composites to machining

temperature, the dicing blade and cutting region of the workpiece were cooled by the coolant system

during the dicing process. Hereby, deionized water was used as coolant. Furthermore, the vibration

of the spindle has an important influence on the micro-cutting damage of CFRP composites, so a

vibration data acquisition system was fixed onto the dicing machine. Two vibration sensors were

adhered onto the surface of spindle with an angle of 90° to perceive the vertical and horizontal

vibrations of the spindle. Because it is difficult to fix a dynamometer onto the cutting machine, the

cutting current was measured to reflect the variation of the cutting force.

As the cutting tool, the dicing blade has a remarkable influence on the cutting quality. Its

preparation method is a key factor for machining performance. The complex preparation process of

the dicing blade includes mixing powders, filling powders into the graphite die, sintering powders,

reducing thickness, and dressing the shape. According to the different matrices in the dicing blade,

the precision dicing blades are divided into three types: metal-sintered diamond blades, resin-bonded

diamond blades, and electroplated nickel bond diamond blades. Metal-sintered diamond blades have

a higher blade lifetime due to the higher thermal conductivity and better mechanical properties of

the binder material. Resin-bonded diamond blades are used in applications that require a smooth

surface finish and a minimum amount of chipping. Electroplated nickel bond diamond blades have

a high diamond concentration and give a freer, faster cutting action with minimum heat generation.

In these cutting experiments, two types of diamond dicing blade, including metal-bonded dicing

blade and resin-bonded dicing blade, were used for cutting CFRP composites. The thicknesses of the

two types of dicing blades were 0.26 ± 0.01 mm and 0.20 ± 0.01 mm, respectively. The diamond size

of dicing blades was about 38 μm, which is much smaller than most of the electroplated diamond

tools used for drilling CFRP laminates. The cross-section structure and the diamond abrasive

distribution of the used dicing blades are shown in Figure 3. It can be seen that the diamond abrasives

distribute uniformly in the blade matrix and has a sharp edge. If the diamond abrasives in the blade

surface wear, they will fall off the blade under the action of cutting force, which is larger than the

bonding force of diamond grits with the matrix. Thus, the diamond blades have better self-

sharpening properties in comparison with PCD (polycrystalline diamond) tools or diamond-coated

cemented carbide tools. The cutting layer area is also much smaller than that of traditional grinding.

Thus, the diamond dicing blade may generate a much smaller cutting force than traditional methods,

which can result in small or free machining damage for CFRP laminates.

Figure 2. Schematic diagram of dicing system for CFRP composites.

As the cutting tool, the dicing blade has a remarkable influence on the cutting quality.Its preparation method is a key factor for machining performance. The complex preparation process ofthe dicing blade includes mixing powders, filling powders into the graphite die, sintering powders,reducing thickness, and dressing the shape. According to the different matrices in the dicing blade,the precision dicing blades are divided into three types: metal-sintered diamond blades, resin-bondeddiamond blades, and electroplated nickel bond diamond blades. Metal-sintered diamond blades havea higher blade lifetime due to the higher thermal conductivity and better mechanical properties of thebinder material. Resin-bonded diamond blades are used in applications that require a smooth surfacefinish and a minimum amount of chipping. Electroplated nickel bond diamond blades have a highdiamond concentration and give a freer, faster cutting action with minimum heat generation. In thesecutting experiments, two types of diamond dicing blade, including metal-bonded dicing blade andresin-bonded dicing blade, were used for cutting CFRP composites. The thicknesses of the two typesof dicing blades were 0.26 ± 0.01 mm and 0.20 ± 0.01 mm, respectively. The diamond size of dicingblades was about 38 µm, which is much smaller than most of the electroplated diamond tools used fordrilling CFRP laminates. The cross-section structure and the diamond abrasive distribution of the useddicing blades are shown in Figure 3. It can be seen that the diamond abrasives distribute uniformly inthe blade matrix and has a sharp edge. If the diamond abrasives in the blade surface wear, they willfall off the blade under the action of cutting force, which is larger than the bonding force of diamondgrits with the matrix. Thus, the diamond blades have better self-sharpening properties in comparisonwith PCD (polycrystalline diamond) tools or diamond-coated cemented carbide tools. The cuttinglayer area is also much smaller than that of traditional grinding. Thus, the diamond dicing blademay generate a much smaller cutting force than traditional methods, which can result in small or freemachining damage for CFRP laminates.

Materials 2018, 11, 1974 5 of 17Materials 2018, 11, x FOR PEER REVIEW 5 of 17

Figure 3. Structure of dicing blade and schematic diagram of cutting process.

In order to demonstrate the influence of the cutting parameters and fiber orientations on cutting

quality, the cutting experiments with different fiber orientations and cutting speeds were conducted

on the dicing machine (Heyan Technology, Shenyang, China) as illustrated in Figure 4. The rotational

speed of the spindle varied from 1000 to 28,000 rpm, in correspondence with the cutting speed from

3 to 85 m/s. The feed speed and cutting depth were 2~4 mm/s and 0.3~0.6 mm, respectively. It can be

observed that the cutting speed is obviously larger than that of most reported machining methods

for CFRP composites. The specimens used for cutting in these experiments were unidirectional T300

CFRP laminates (Shenyang Aircraft Corporation, Shenyang, China). After the cutting process, the

sliced sections of CFRP laminates were observed with an optical microscope (Shanghai Optical

Instrument Co., LTD., Shanghai, China) and SEM (Hitachi High-Technologies Corporation, Tokyo,

Japan) to characterize the dicing damage in different dicing conditions.

Figure 4. Schematic diagram of cutting direction and cutting parameters.

3. Results, Analysis, and Discussion

3.1. Influence of Different Cutting Speeds on Cutting Quality

Just like other nature fiber composites with heterogeneous and anisotropic properties, the

cutting quality of CFRP composites is also very sensitive to the cutting speed. In low cutting speeds,

the fibers embedded in the matrix are easy to bend so as to cause large machining damage, such as

delamination and debonding [46]. High machining speeds over 40 m/s can generate good surface

quality for wood and other fiber reinforced composites [48]. In this study, the cutting current of the

spindle and surface roughness are observed to characterize the influence of cutting speed. Many

studies on the relation between the cutting force and the motor current [49] proved that the change

of spindle motor current value reflects the cutting force well, and cutting force obtained by measuring

the spindle motor current is reasonable and feasible. Due to the limited working space in the dicing

machine, it is difficult to place a dynamometer onto the worktable to detect the cutting force. Thus,

in this experiment, the cutting current obtained from the spindle motor was employed to study the

change of cutting force with different cutting conditions. As illustrated in Figure 5, the cutting current


In order to demonstrate the influence of the cutting parameters and fiber orientations on cuttingquality, the cutting experiments with different fiber orientations and cutting speeds were conductedon the dicing machine (Heyan Technology, Shenyang, China) as illustrated in Figure 4. The rotationalspeed of the spindle varied from 1000 to 28,000 rpm, in correspondence with the cutting speed from 3to 85 m/s. The feed speed and cutting depth were 2~4 mm/s and 0.3~0.6 mm, respectively. It can beobserved that the cutting speed is obviously larger than that of most reported machining methods forCFRP composites. The specimens used for cutting in these experiments were unidirectional T300 CFRPlaminates (Shenyang Aircraft Corporation, Shenyang, China). After the cutting process, the slicedsections of CFRP laminates were observed with an optical microscope (Shanghai Optical InstrumentCo., LTD., Shanghai, China) and scanning electron microscope (SEM, Hitachi High-TechnologiesCorporation, Tokyo, Japan) to characterize the dicing damage in different dicing conditions.



In order to demonstrate the influence of the cutting parameters and fiber orientations on cutting

quality, the cutting experiments with different fiber orientations and cutting speeds were conducted

on the dicing machine (Heyan Technology, Shenyang, China) as illustrated in Figure 4. The rotational

speed of the spindle varied from 1000 to 28,000 rpm, in correspondence with the cutting speed from

3 to 85 m/s. The feed speed and cutting depth were 2~4 mm/s and 0.3~0.6 mm, respectively. It can be

observed that the cutting speed is obviously larger than that of most reported machining methods

for CFRP composites. The specimens used for cutting in these experiments were unidirectional T300

CFRP laminates (Shenyang Aircraft Corporation, Shenyang, China). After the cutting process, the

sliced sections of CFRP laminates were observed with an optical microscope (Shanghai Optical

Instrument Co., LTD., Shanghai, China) and SEM (Hitachi High-Technologies Corporation, Tokyo,

Japan) to characterize the dicing damage in different dicing conditions.




Just like other nature fiber composites with heterogeneous and anisotropic properties, the

cutting quality of CFRP composites is also very sensitive to the cutting speed. In low cutting speeds,

the fibers embedded in the matrix are easy to bend so as to cause large machining damage, such as

delamination and debonding [46]. High machining speeds over 40 m/s can generate good surface

quality for wood and other fiber reinforced composites [48]. In this study, the cutting current of the

spindle and surface roughness are observed to characterize the influence of cutting speed. Many

studies on the relation between the cutting force and the motor current [49] proved that the change

of spindle motor current value reflects the cutting force well, and cutting force obtained by measuring

the spindle motor current is reasonable and feasible. Due to the limited working space in the dicing

machine, it is difficult to place a dynamometer onto the worktable to detect the cutting force. Thus,

in this experiment, the cutting current obtained from the spindle motor was employed to study the

change of cutting force with different cutting conditions. As illustrated in Figure 5, the cutting current




Just like other nature fiber composites with heterogeneous and anisotropic properties, the cuttingquality of CFRP composites is also very sensitive to the cutting speed. In low cutting speeds, the fibersembedded in the matrix are easy to bend so as to cause large machining damage, such as delaminationand debonding [46]. High machining speeds over 40 m/s can generate good surface quality for woodand other fiber reinforced composites [48]. In this study, the cutting current of the spindle and surfaceroughness are observed to characterize the influence of cutting speed. Many studies on the relationbetween the cutting force and the motor current [49] proved that the change of spindle motor currentvalue reflects the cutting force well, and cutting force obtained by measuring the spindle motor currentis reasonable and feasible. Due to the limited working space in the dicing machine, it is difficultto place a dynamometer onto the worktable to detect the cutting force. Thus, in this experiment,the cutting current obtained from the spindle motor was employed to study the change of cuttingforce with different cutting conditions. As illustrated in Figure 5, the cutting current of the spindle

Materials 2018, 11, 1974 6 of 17

motor first increased with the rotational speed of the spindle and then decreased under the conditionof no-load. The cutting current under the cutting condition has a similar trend of that of no-load.The difference is that there is an obvious increase when the spindle rotational speed changes from25,000 to 28,000 rpm under the cutting condition. It indicates that under rotational speeds higher than25,000 rpm, the cutting resistance increases enormously. High cutting current in the rotational speed of4000 rpm attributes to the self-excited chatter vibrations of the spindle. Under the condition of lowrotational speeds, the cutting layer area is larger than that of high rotational speeds. Cutting force andcutting current therefore increases in low rotational speeds.


of the spindle motor first increased with the rotational speed of the spindle and then decreased under

the condition of no-load. The cutting current under the cutting condition has a similar trend of that

of no-load. The difference is that there is an obvious increase when the spindle rotational speed

changes from 25,000 to 28,000 rpm under the cutting condition. It indicates that under rotational

speeds higher than 25,000 rpm, the cutting resistance increases enormously. High cutting current in

the rotational speed of 4000 rpm attributes to the self-excited chatter vibrations of the spindle. Under

the condition of low rotational speeds, the cutting layer area is larger than that of high rotational

speeds. Cutting force and cutting current therefore increases in low rotational speeds.

1.55

1.60

1.65

1.70

1.75

1.80

1.85

1.90

28,00025,000

22,00019,000

16,00013,000

10,0007000

4000

Cutt

ing c

urr

ent

(A)

Spindle rotational speed (rpm)

Conditions

No-load

Feed speed Vf = 2mm/s

Cutting depth ap = 0.3mm

Coolant flow VL= 2.5L/min

Dicing with metal bonded diamond blade

1000

Figure 5. Maximum cutting current varying with spindle rotational speed.

As presented in Figure 6, the surface roughness of machined CFRP laminates appears to have

the same tendency as the cutting current, which illustrates that there is a significant correlation

between cutting current and surface roughness. According to previous studies, the cutting current

can reflect the cutting force reasonably. Thus, small cutting forces will generate lower surface

roughness. It can conclude that CFRP laminates present the best cutting quality at the rotationl speed

of 25,000 rpm where the spindle motor runs steadily. Too high rotational speeds of the spindle are

not beneficial in improving the dicing quality of CFRP laminates. Meanwhile, the deformation of the

dicing blade and vibration of the spindle in low rotational speeds increases the surface roughness of

CFRP laminates.

0.0

0.1

0.2

0.3

0.4

0.5

Surf

ace r

ough

ness R

a (m

)

Spindle rotational speed n (rpm)




Coolant flow VL = 2.5L/min

28,00025,000

22,00019,000

16,00013,000

10,0007000

40001000

Figure 6. Surface roughness varying with spindle rotational speed.

Because the thickness of the dicing blade is very thin in comparison with the traditional grinding

wheel, it is easy to deform or even break under the cutting force. In order to prevent it breaking,

increasing the rotational speed is an effective method to shift the dynamic stiffness of the dicing blade.


As presented in Figure 6, the surface roughness of machined CFRP laminates appears to have thesame tendency as the cutting current, which illustrates that there is a significant correlation betweencutting current and surface roughness. According to previous studies, the cutting current can reflectthe cutting force reasonably. Thus, small cutting forces will generate lower surface roughness. It canconclude that CFRP laminates present the best cutting quality at the rotationl speed of 25,000 rpmwhere the spindle motor runs steadily. Too high rotational speeds of the spindle are not beneficial inimproving the dicing quality of CFRP laminates. Meanwhile, the deformation of the dicing blade andvibration of the spindle in low rotational speeds increases the surface roughness of CFRP laminates.


of the spindle motor first increased with the rotational speed of the spindle and then decreased under

the condition of no-load. The cutting current under the cutting condition has a similar trend of that

of no-load. The difference is that there is an obvious increase when the spindle rotational speed

changes from 25,000 to 28,000 rpm under the cutting condition. It indicates that under rotational

speeds higher than 25,000 rpm, the cutting resistance increases enormously. High cutting current in

the rotational speed of 4000 rpm attributes to the self-excited chatter vibrations of the spindle. Under

the condition of low rotational speeds, the cutting layer area is larger than that of high rotational

speeds. Cutting force and cutting current therefore increases in low rotational speeds.

1.55

1.60

1.65

1.70

1.75

1.80

1.85

1.90

28,00025,000

22,00019,000

16,00013,000

10,0007000

4000

Cutt

ing c

urr

ent

(A)

Spindle rotational speed (rpm)

Conditions

No-load



Coolant flow VL= 2.5L/min


1000


As presented in Figure 6, the surface roughness of machined CFRP laminates appears to have

the same tendency as the cutting current, which illustrates that there is a significant correlation

between cutting current and surface roughness. According to previous studies, the cutting current

can reflect the cutting force reasonably. Thus, small cutting forces will generate lower surface

roughness. It can conclude that CFRP laminates present the best cutting quality at the rotationl speed

of 25,000 rpm where the spindle motor runs steadily. Too high rotational speeds of the spindle are

not beneficial in improving the dicing quality of CFRP laminates. Meanwhile, the deformation of the

dicing blade and vibration of the spindle in low rotational speeds increases the surface roughness of

CFRP laminates.

0.0

0.1

0.2

0.3

0.4

0.5

Su

rfa

ce r

oug

hness R

a (m

)

Spindle rotational speed n (rpm)




Coolant flow VL = 2.5L/min

28,00025,000

22,00019,000

16,00013,000

10,0007000

40001000


Because the thickness of the dicing blade is very thin in comparison with the traditional grinding

wheel, it is easy to deform or even break under the cutting force. In order to prevent it breaking,

increasing the rotational speed is an effective method to shift the dynamic stiffness of the dicing blade.


Because the thickness of the dicing blade is very thin in comparison with the traditional grindingwheel, it is easy to deform or even break under the cutting force. In order to prevent it breaking,

Materials 2018, 11, 1974 7 of 17

increasing the rotational speed is an effective method to shift the dynamic stiffness of the dicingblade. Therefore, the thin dicing blade does not deform like paper during the cutting process. If thedicing blade is regarded as a hollow disk with a rectangular section, according to the theory of solidmechanics, the maximum stress and displacement of the dicing blade can be calculated with thefollowing equations.

σr =3 + µ

8ρω2

(r2

0 + r2i − r2 −

r20r2

ir2

), (1)

στ =3 + µ

8ρω2

(r2

0 + r2i −

1 + 3µ

1− 3µr2 +

r20r2

ir2

), (2)

u =1− µ2

8Eσω2

[3 + µ

1 + µ

(r2

0 + r2i

)r +

(3 + µ

1− µ

)r2

0r2i

r2 − r3

], (3)

where, r =√

r0ri, σr, στ and u are radial stress, circumferential stress, and displacement, respectively.µ, ρ, and E are the Poisson’s ratio, density, and elasticity modulus of the dicing blade, respectively.Because the diamond abrasive dicing blade is made of typical heterogenetic materials, it is difficult tocalculate the above parameters accurately. Thus, in this study the average values of Poisson’s ratio,density, and elasticity modulus are estimated as 0.22, 5.1 × 103 kg/m3, and 128 GPa in considerationof the proportion of diamond abrasive and matrix.

Figure 7 shows the simulation results of circumferential stress, radial stress, and displacementof the dicing blade. With the increase of rotational speed, circumferential stress and displacement ofdicing blade increase remarkably. High circumferential stress spreads the dicing blade to ensure thatthe dicing blade has enough rigidity, although it is so thin like paper. It effectively prevents the dicingblade from large deformations under the interactions of the cutting force. That is the reason why thecutting quality of CFRP composites is better at high rotational speeds. Also, it may be a preconditionfor micro-cutting CFRP laminates with an ultra-thin dicing blade.


Therefore, the thin dicing blade does not deform like paper during the cutting process. If the dicing

blade is regarded as a hollow disk with a rectangular section, according to the theory of solid

mechanics, the maximum stress and displacement of the dicing blade can be calculated with the

following equations.

2 2

2 2 2 2 0

0 2

3

8

i

r i

r rr r r

r

, (1)

2 2

2 2 2 2 0

0 2

3 1 3

8 1 3

i

i

r rr r r

r

, (2)

2 22

2 2 2 30

0 2

1 3 3

8 1 1

i

i

r ru r r r r

E r

, (3)

where, 0 ir r r , σr, στ and u are radial stress, circumferential stress, and displacement, respectively.

μ, ρ, and E are the Poisson's ratio, density, and elasticity modulus of the dicing blade, respectively.

Because the diamond abrasive dicing blade is made of typical heterogenetic materials, it is difficult

to calculate the above parameters accurately. Thus, in this study the average values of Poisson’s ratio,

density, and elasticity modulus are estimated as 0.22, 5.1 × 103 kg/m3, and 128 GPa in consideration

of the proportion of diamond abrasive and matrix.

Figure 7 shows the simulation results of circumferential stress, radial stress, and displacement

of the dicing blade. With the increase of rotational speed, circumferential stress and displacement of

dicing blade increase remarkably. High circumferential stress spreads the dicing blade to ensure that

the dicing blade has enough rigidity, although it is so thin like paper. It effectively prevents the dicing

blade from large deformations under the interactions of the cutting force. That is the reason why the

cutting quality of CFRP composites is better at high rotational speeds. Also, it may be a precondition

for micro-cutting CFRP laminates with an ultra-thin dicing blade.

0 5,000 10,000 15,000 20,000 25,00030,000 35,000

0

5

10

15

20

25

30

35

40

45

50

55

60

Dis

pla

ce

me

nt

of

dic

ing

bla

de

(m

)

Ma

xim

um

str

ess o

f d

icin

g b

lad

e (

MP

a)

Rotational Speed n (r/min)

Circumferential stress

Radial stress

Circumferential stress

distribution

Radial stress

distribution

5000

0.000

0.005

0.010

0.015

0.020 Displacement

Displacement

disribution

Figure 7. Maximum stress and displacement of the dicing blade with different rotational speed.

3.2. Influence of Spindle Vibration on Cutting Quality of CFRP Laminates

The main mechanisms generating excessive cutting tool vibration can be classified into three

types: regenerative, mode coupling, and velocity-dependent [50]. Velocity-dependent mainly

originates from the self-excited chatter vibrations of spindle. When the rotational speed is about 4000

rpm, the resonance of the spindle drives the large vibration of the cutting tool, which therefore results

in large cutting surface roughness. The regenerative vibration has a simple relationship between the

cutting force coefficient, dynamic stiffness of the structure, spindle speed, and depth of cut [51]. The

vibration stability has been attributed to either the change in the direction of cutting speed or the

cutting force between the cutting tool and the finished workpiece. During the cutting process with

Figure 7. Maximum stress and displacement of the dicing blade with different rotational speed.

3.2. Influence of Spindle Vibration on Cutting Quality of CFRP Laminates

The main mechanisms generating excessive cutting tool vibration can be classified into three types:regenerative, mode coupling, and velocity-dependent [50]. Velocity-dependent mainly originatesfrom the self-excited chatter vibrations of spindle. When the rotational speed is about 4000 rpm,the resonance of the spindle drives the large vibration of the cutting tool, which therefore resultsin large cutting surface roughness. The regenerative vibration has a simple relationship betweenthe cutting force coefficient, dynamic stiffness of the structure, spindle speed, and depth of cut [51].

Materials 2018, 11, 1974 8 of 17

The vibration stability has been attributed to either the change in the direction of cutting speed orthe cutting force between the cutting tool and the finished workpiece. During the cutting processwith the dicing blade, the cutting speed is located in the direction normal to the axis of the spindle.Furthermore, the cutting force can be divided into two component forces in vertical and horizontaldirections. Thus, the vibrations in the vertical and horizontal directions are obvious. When therotational speed increases to 28,000 rpm from 25,000 rpm, the vibration in the horizontal direction has asignificant increase, as shown in Figure 8. It demonstrates that the large surface roughness and cuttingcurrent is mainly caused by the vibration in the horizontal direction. The vibration of the spindle inthe vertical direction is small due to the weight of the spindle and the load shift in the stiffness of thespindle in the vertical direction. Besides, the change of the cutting force in the horizontal direction dueto the heterogeneity between the fiber and resin matrix can also be attributed to the large vibration.Other cutting parameters, such as feed speed and cutting depth, have a small effect on the vibrationamplitude of the spindle. As shown in Figure 8c, there is a slight increase of vibration amplitude in thevertical direction when the cutting depth changes from 0.2 to 0.8 mm, while the vibration amplitude ofthe spindle in the horizontal direction keeps a steady change varying with the cutting parameters.


the dicing blade, the cutting speed is located in the direction normal to the axis of the spindle.

Furthermore, the cutting force can be divided into two component forces in vertical and horizontal

directions. Thus, the vibrations in the vertical and horizontal directions are obvious. When the

rotational speed increases to 28,000 rpm from 25,000 rpm, the vibration in the horizontal direction

has a significant increase, as shown in Figure 8. It demonstrates that the large surface roughness and

cutting current is mainly caused by the vibration in the horizontal direction. The vibration of the

spindle in the vertical direction is small due to the weight of the spindle and the load shift in the

stiffness of the spindle in the vertical direction. Besides, the change of the cutting force in the

horizontal direction due to the heterogeneity between the fiber and resin matrix can also be attributed

to the large vibration. Other cutting parameters, such as feed speed and cutting depth, have a small

effect on the vibration amplitude of the spindle. As shown in Figure 8c, there is a slight increase of

vibration amplitude in the vertical direction when the cutting depth changes from 0.2 to 0.8 mm,

while the vibration amplitude of the spindle in the horizontal direction keeps a steady change varying

with the cutting parameters.

15,000 20,000 25,000 30,000

0

5

10

15

20

25

30

Accele

ration

am

plit

ud

e (

m/s

2)

Rotational speed (rpm)

Vertical, conditions

Horizontal, no-load

Vertical, no-load

Horizontal, conditions

2 4 6 8

1.5

2.0

2.5

3.0

3.5

4.0

4.5

5.0

5.5

6.0

Accele

ration

am

plitu

de (

m/s

2)

Feed speed (mm/s)



0.2 0.4 0.6 0.8

1.5

2.0

2.5

3.0

3.5

4.0

4.5

5.0

5.5

6.0

Accele

ration

am

plit

ud

e (

m/s

2)

Cutting depth (mm)



(a) Rotational speed (b) Feed speed (c) Cutting depth

Figure 8. Vibration acceleration amplitude varying with cutting parameters in time domain.

Figure 9 illustrates the vibration acceleration spectrum diagram with different conditions in

frequency domain. As can be seen from the figures, the vibration amplitudes under the condition of

cutting are a little larger than the vibration amplitudes under the condition of no-load. It indicates

that the cutting force has a weak effect on the vibration of the spindle because the cutting force

generated by the ultra-thin dicing blade is very small at high rotational speeds. However, it should

be noted that the vibration amplitudes under the rotational speed of 30,000 rpm are apparently more

serious than that of 25,000 rpm. The serious vibration also results in larger surface roughness of CFRP

laminates after cutting with the dicing blade. Moreover, there is no new vibration frequency to create

by comparing cutting conditions with the no-load condition. The vibration during the cutting process

mainly derives from the spindle motor and the dicing machine itself but not the cutting force. The

promotion of a small cutting force generated by the dicing blade to the vibration of the spindle is very

weak, although the vibration plays a remarkable role on the surface roughness of CFRP laminates.


Figure 9 illustrates the vibration acceleration spectrum diagram with different conditions infrequency domain. As can be seen from the figures, the vibration amplitudes under the condition ofcutting are a little larger than the vibration amplitudes under the condition of no-load. It indicates thatthe cutting force has a weak effect on the vibration of the spindle because the cutting force generated bythe ultra-thin dicing blade is very small at high rotational speeds. However, it should be noted that thevibration amplitudes under the rotational speed of 30,000 rpm are apparently more serious than thatof 25,000 rpm. The serious vibration also results in larger surface roughness of CFRP laminates aftercutting with the dicing blade. Moreover, there is no new vibration frequency to create by comparingcutting conditions with the no-load condition. The vibration during the cutting process mainly derivesfrom the spindle motor and the dicing machine itself but not the cutting force. The promotion of asmall cutting force generated by the dicing blade to the vibration of the spindle is very weak, althoughthe vibration plays a remarkable role on the surface roughness of CFRP laminates.

Materials 2018, 11, 1974 9 of 17


the dicing blade, the cutting speed is located in the direction normal to the axis of the spindle.

Furthermore, the cutting force can be divided into two component forces in vertical and horizontal

directions. Thus, the vibrations in the vertical and horizontal directions are obvious. When the

rotational speed increases to 28,000 rpm from 25,000 rpm, the vibration in the horizontal direction

has a significant increase, as shown in Figure 8. It demonstrates that the large surface roughness and

cutting current is mainly caused by the vibration in the horizontal direction. The vibration of the

spindle in the vertical direction is small due to the weight of the spindle and the load shift in the

stiffness of the spindle in the vertical direction. Besides, the change of the cutting force in the

horizontal direction due to the heterogeneity between the fiber and resin matrix can also be attributed

to the large vibration. Other cutting parameters, such as feed speed and cutting depth, have a small

effect on the vibration amplitude of the spindle. As shown in Figure 8c, there is a slight increase of

vibration amplitude in the vertical direction when the cutting depth changes from 0.2 to 0.8 mm,

while the vibration amplitude of the spindle in the horizontal direction keeps a steady change varying

with the cutting parameters.

15,000 20,000 25,000 30,000

0

5

10

15

20

25

30

Accele

ration

am

plit

ud

e (

m/s

2)

Rotational speed (rpm)


Horizontal, no-load

Vertical, no-load


2 4 6 8

1.5

2.0

2.5

3.0

3.5

4.0

4.5

5.0

5.5

6.0

Accele

ration

am

plitu

de (

m/s

2)

Feed speed (mm/s)



0.2 0.4 0.6 0.8

1.5

2.0

2.5

3.0

3.5

4.0

4.5

5.0

5.5

6.0

Accele

ration

am

plit

ud

e (

m/s

2)

Cutting depth (mm)



(a) Rotational speed (b) Feed speed (c) Cutting depth


Figure 9 illustrates the vibration acceleration spectrum diagram with different conditions in

frequency domain. As can be seen from the figures, the vibration amplitudes under the condition of

cutting are a little larger than the vibration amplitudes under the condition of no-load. It indicates

that the cutting force has a weak effect on the vibration of the spindle because the cutting force

generated by the ultra-thin dicing blade is very small at high rotational speeds. However, it should

be noted that the vibration amplitudes under the rotational speed of 30,000 rpm are apparently more

serious than that of 25,000 rpm. The serious vibration also results in larger surface roughness of CFRP

laminates after cutting with the dicing blade. Moreover, there is no new vibration frequency to create

by comparing cutting conditions with the no-load condition. The vibration during the cutting process

mainly derives from the spindle motor and the dicing machine itself but not the cutting force. The

promotion of a small cutting force generated by the dicing blade to the vibration of the spindle is very

weak, although the vibration plays a remarkable role on the surface roughness of CFRP laminates.


Figure 9. Vibration acceleration spectrum diagram with different conditions in frequency domain. (a)

With a rotational speed of 25,000 rpm and no-load condition; (b) with a rotational speed of 25,000 rpm

and conditions, (c) with a rotational speed of 30,000 rpm and no-load condition; (d) with a rotational

speed of 30,000 rpm and conditions.

3.3. Influence of Fiber Orientations on Dicing Quality

The fiber orientations have remarkable influence on the cutting current and surface quality due

to the outstanding anisotropy of CFRP laminates. Figure 10 shows the maximum cutting current of

the spindle motor when different fiber orientation laminates are cut with the resin-bonded dicing

blade and the metal-bonded dicing blade. It can be noted that the cutting current of the spindle motor

with the metal-bonded dicing blade are overall smaller than that of with the resin-bonded dicing

blade, which is different from the cutting of regular brittle materials, such as glass. When cutting

brittle materials, the cutting force with a resin-bonded blade is usually smaller than the metal-bonded

blade due to the small bonding force of diamond grits with resin matrix. For cutting CFRP composites

in this experiment, the poor thermal conductivity of the resin-bonded blade and the CFRP workpiece

led to the increase in cutting temperature and the softening of the resin, which results in shifting the

cutting force. Therefore, the large cutting force generates a larger cutting current with the resin-

bonded blade and causes more serious wear to the dicing blade. It can be verified by the results of

the cutting experiments. The wear amounts of the resin-bonded blade in the diameter direction is

about 0.17 mm per cutting 10 m, while the wear amounts of the metal-bonded blade is about 0.13 mm

per cutting 10 m.

The cutting currents of the spindle motor present an overall V-shape tendency when the fiber

orientation angle changes from 0° to 180°. The minimum cutting current occurs at the fiber orientation

of 90°. That is to say that cutting along with fiber orientation can generate a maximum cutting current,

and cutting perpendicular to fiber orientation can generate a minimum cutting current. Moreover,

there are two low points at the fiber orientations of about 40° and 140°. All these tendencies are

contrary to most reported results of milling and orthogonal cutting of CFRP composites [19,20].

Usually the cutting force will increase with the fiber orientation as it changes from 0° to 90°. The

differences can be attributed to the different cutting mechanisms between dicing and milling or

orthogonal cutting. During the milling and orthogonal cutting, the feed rate or feed per tooth is far

larger than the diameter of a fiber. Many fibers, together with the resin matrix, are cut down at one

time [52]. It results in the carbon fibers and resin matrix undergoing serious deformation under the

large cutting force generated by the large tool edge radius. However, for dicing CFRP composites

with the diamond dicing blade, the feed rate can be calculated at about 9.6 μm/r. Additionally, there

are more than one thousand diamond grits that participate in the cutting in the circumference of a

dicing blade. Thus, the feed rate per grit is no more than 0.0096 μm, which is far smaller than the

diameter of carbon fiber. With the small cutting depth, the cutting action or material removal only

occurs at the local regions of carbon fiber or resin matrix. It cannot cause large deformation to the

fibers or resin matrix. Thus, the cutting damage is limited in a small region correspondingly and a

fine machined surface is obtained.

Figure 9. Vibration acceleration spectrum diagram with different conditions in frequency domain.(a) With a rotational speed of 25,000 rpm and no-load condition; (b) with a rotational speed of 25,000 rpmand conditions, (c) with a rotational speed of 30,000 rpm and no-load condition; (d) with a rotationalspeed of 30,000 rpm and conditions.

3.3. Influence of Fiber Orientations on Dicing Quality

The fiber orientations have remarkable influence on the cutting current and surface quality due tothe outstanding anisotropy of CFRP laminates. Figure 10 shows the maximum cutting current of thespindle motor when different fiber orientation laminates are cut with the resin-bonded dicing bladeand the metal-bonded dicing blade. It can be noted that the cutting current of the spindle motor withthe metal-bonded dicing blade are overall smaller than that of with the resin-bonded dicing blade,which is different from the cutting of regular brittle materials, such as glass. When cutting brittlematerials, the cutting force with a resin-bonded blade is usually smaller than the metal-bonded bladedue to the small bonding force of diamond grits with resin matrix. For cutting CFRP composites inthis experiment, the poor thermal conductivity of the resin-bonded blade and the CFRP workpieceled to the increase in cutting temperature and the softening of the resin, which results in shifting thecutting force. Therefore, the large cutting force generates a larger cutting current with the resin-bondedblade and causes more serious wear to the dicing blade. It can be verified by the results of the cuttingexperiments. The wear amounts of the resin-bonded blade in the diameter direction is about 0.17 mmper cutting 10 m, while the wear amounts of the metal-bonded blade is about 0.13 mm per cutting 10 m.Materials 2018, 11, x FOR PEER REVIEW 10 of 17

0 20 40 60 80 100 120 140 160 180

1.705

1.710

1.715

1.720

1.725

1.730

1.735

1.740

1.745

1.750

Cu

ttin

g c

urr

en

t (A

)

Fiber orientation angles ()

Resin bonded dicing blade

Metal bonded dicing blade

Cutting speed Vc = 76m/s



Coolant flow rate VL = 2.5L/min

Figure 10. Maximum cutting current varying with fiber orientation.

Figure 11 gives the surface roughness of machined CFRP composites varying with the fiber

orientation. It is interesting that the tendency of the surface roughness changing with fiber orientation

is very similar to that of the cutting current. It illustrates that the surface roughness of diced CFRP

composites has a significant correlation with cutting force. When the cutting direction is vertical to

fiber orientation, the surface roughness of machined CFRP composites is smallest, which is about Ra

0.025 μm, better than most reported experimental results with drilling, milling, or grinding methods.

The fiber orientations of 50° and 130° also achieve a relatively better diced surface, while the surface

roughness is worst when the fiber orientation is 0° or 180°. These tendencies are also different from

traditional milling and drilling processes just as is the cutting current of the spindle motor.

Furthermore, the metal-bonded dicing blade generates better surface roughness than the resin-

bonded dicing blade, mainly due to its low cutting force and good thermal conductivity.

0 20 40 60 80 100 120 140 160 1800.00

0.05

0.10

0.15

0.20

0.25

Su

rfa

ce

ro

ug

hn

ess R

a (m

)

Fiber orientation angle ()







Figure 11. Surface roughness varying with fiber orientation.

In order to address the reason of the above tendency of surface roughness, surface morphologies

of diced CFRP composites with different fiber orientations are investigated, as shown in Figure 12.

As can be seen from the figures, the surface qualities of diced CFRP composites with the metal-

bonded dicing blade are better than that of the resin-bonded dicing blade. According to the

observations of cutting morphologies, one of main reasons causing large surface roughness with the

resin-bonded dicing blade is that there is some molten resin on the machined surface of CFRP

composites. It reflects that the high dicing temperature occurs during this process. Under the high

temperature, a lot of molten resin adheres to the dicing blade and the machined surface, which not

only reduces the cutting performance of the dicing blade, but also increases the machined surface

roughness of CFRP composites and the cutting force. In view of cutting CFRP composites with 0°

fiber orientations as shown in Figure 12a,e, the fibers have been cut off along their axis. The machined


Materials 2018, 11, 1974 10 of 17

The cutting currents of the spindle motor present an overall V-shape tendency when the fiberorientation angle changes from 0◦ to 180◦. The minimum cutting current occurs at the fiber orientationof 90◦. That is to say that cutting along with fiber orientation can generate a maximum cutting current,and cutting perpendicular to fiber orientation can generate a minimum cutting current. Moreover, thereare two low points at the fiber orientations of about 40◦ and 140◦. All these tendencies are contraryto most reported results of milling and orthogonal cutting of CFRP composites [19,20]. Usually thecutting force will increase with the fiber orientation as it changes from 0◦ to 90◦. The differences canbe attributed to the different cutting mechanisms between dicing and milling or orthogonal cutting.During the milling and orthogonal cutting, the feed rate or feed per tooth is far larger than the diameterof a fiber. Many fibers, together with the resin matrix, are cut down at one time [52]. It results in thecarbon fibers and resin matrix undergoing serious deformation under the large cutting force generatedby the large tool edge radius. However, for dicing CFRP composites with the diamond dicing blade,the feed rate can be calculated at about 9.6 µm/r. Additionally, there are more than one thousanddiamond grits that participate in the cutting in the circumference of a dicing blade. Thus, the feed rateper grit is no more than 0.0096 µm, which is far smaller than the diameter of carbon fiber. With thesmall cutting depth, the cutting action or material removal only occurs at the local regions of carbonfiber or resin matrix. It cannot cause large deformation to the fibers or resin matrix. Thus, the cuttingdamage is limited in a small region correspondingly and a fine machined surface is obtained.

Figure 11 gives the surface roughness of machined CFRP composites varying with the fiberorientation. It is interesting that the tendency of the surface roughness changing with fiber orientationis very similar to that of the cutting current. It illustrates that the surface roughness of diced CFRPcomposites has a significant correlation with cutting force. When the cutting direction is vertical tofiber orientation, the surface roughness of machined CFRP composites is smallest, which is about Ra0.025 µm, better than most reported experimental results with drilling, milling, or grinding methods.The fiber orientations of 50◦ and 130◦ also achieve a relatively better diced surface, while the surfaceroughness is worst when the fiber orientation is 0◦ or 180◦. These tendencies are also different fromtraditional milling and drilling processes just as is the cutting current of the spindle motor. Furthermore,the metal-bonded dicing blade generates better surface roughness than the resin-bonded dicing blade,mainly due to its low cutting force and good thermal conductivity.


0 20 40 60 80 100 120 140 160 180

1.705

1.710

1.715

1.720

1.725

1.730

1.735

1.740

1.745

1.750

Cu

ttin

g c

urr

en

t (A

)

Fiber orientation angles ()








Figure 11 gives the surface roughness of machined CFRP composites varying with the fiber

orientation. It is interesting that the tendency of the surface roughness changing with fiber orientation

is very similar to that of the cutting current. It illustrates that the surface roughness of diced CFRP

composites has a significant correlation with cutting force. When the cutting direction is vertical to

fiber orientation, the surface roughness of machined CFRP composites is smallest, which is about Ra

0.025 μm, better than most reported experimental results with drilling, milling, or grinding methods.

The fiber orientations of 50° and 130° also achieve a relatively better diced surface, while the surface

roughness is worst when the fiber orientation is 0° or 180°. These tendencies are also different from

traditional milling and drilling processes just as is the cutting current of the spindle motor.

Furthermore, the metal-bonded dicing blade generates better surface roughness than the resin-

bonded dicing blade, mainly due to its low cutting force and good thermal conductivity.

0 20 40 60 80 100 120 140 160 1800.00

0.05

0.10

0.15

0.20

0.25

Su

rfa

ce

ro

ug

hn

ess R

a (m

)









In order to address the reason of the above tendency of surface roughness, surface morphologies

of diced CFRP composites with different fiber orientations are investigated, as shown in Figure 12.

As can be seen from the figures, the surface qualities of diced CFRP composites with the metal-

bonded dicing blade are better than that of the resin-bonded dicing blade. According to the

observations of cutting morphologies, one of main reasons causing large surface roughness with the

resin-bonded dicing blade is that there is some molten resin on the machined surface of CFRP

composites. It reflects that the high dicing temperature occurs during this process. Under the high

temperature, a lot of molten resin adheres to the dicing blade and the machined surface, which not

only reduces the cutting performance of the dicing blade, but also increases the machined surface

roughness of CFRP composites and the cutting force. In view of cutting CFRP composites with 0°

fiber orientations as shown in Figure 12a,e, the fibers have been cut off along their axis. The machined


In order to address the reason of the above tendency of surface roughness, surface morphologies ofdiced CFRP composites with different fiber orientations are investigated, as shown in Figure 12. As canbe seen from the figures, the surface qualities of diced CFRP composites with the metal-bonded dicingblade are better than that of the resin-bonded dicing blade. According to the observations of cuttingmorphologies, one of main reasons causing large surface roughness with the resin-bonded dicing bladeis that there is some molten resin on the machined surface of CFRP composites. It reflects that the

Materials 2018, 11, 1974 11 of 17

high dicing temperature occurs during this process. Under the high temperature, a lot of molten resinadheres to the dicing blade and the machined surface, which not only reduces the cutting performanceof the dicing blade, but also increases the machined surface roughness of CFRP composites and thecutting force. In view of cutting CFRP composites with 0◦ fiber orientations as shown in Figure 12a,e,the fibers have been cut off along their axis. The machined surface of the left-half sections presentsvery good quality in a small region. But not all fibers are strictly embedded in the direction parallelto the machining surface. The fibers not well embedded in the resin matrix will debond from thematrix due to the poor bonding strength of half fiber. The left grooves cause a larger measured surfaceroughness than other fiber orientations. When the CFRP composite is sliced at 90◦ fiber orientation,the fibers are cut smoothly due to the well fixation of fibers in the matrix, according to Figure 12c,g.They have not undergone serious deformation under the cutting force, like milling or drilling. Duringthe milling or drilling process, bunches of fibers bend under the cutting force and finally break toform a zigzag or uneven cutting section [22]. Fiber-tensile failure and matrix-compression failure arenormally used to explain the cutting mechanism for these methods [53]. The microtopography of themachined surface of CFRP with the dicing blade shows its cutting mechanisms are different from thatof milling and drilling. Furthermore, as shown in Figure 12b,f,d,h, there are lot of micro fractureson the machined section of CFRP composites when cutting with 40◦ fiber orientation and 130◦ fiberorientation, although the machined surface is very even. Most of these micro fractures are located at aright position of the fiber section when cutting with 40◦ fiber orientation, and at a left position of thefiber section when cutting with 130◦ fiber orientation. All these positions are at the wedge tip of fiberends, and the material strength is poor. It is easy for the materials at the tip of the fiber to break offunder the actions of cutting force and vibration. Thus, the surface roughness cutting at 40◦ or 130◦

fiber orientation is larger than that of 90◦ fiber orientation. Besides the micro fracture, it should benoted that there are slight fiber debondings with the resin matrix when cutting with 40◦ and 130◦ fiberorientations. It means that the fibers bend towards the fiber bundle extrusion. But this debondingbetween fiber and matrix is far weaker than other methods. That is to say that a very smooth machinedsurface can be obtained when the cutting depth is smaller than the diameter of fibers. No seriousmaterial damage, such as delamination, burrs, fiber pull out, are detected, although obtained surfaceroughness is larger than cutting traditional brittle materials.


Figure 12. Surface morphologies of CFRP composites after dicing with different fiber orientation.

Figure 13. Schematic diagram of scratching CFRP composites with diamond indenter.

0 30 60 90 120 150 180 210 240 270 300 330 3600

2

4

6

8

10

12

14

16

18

120 indenter, F z = 10N


120 indenter, F z = 20N 60 indenter, F z = 10N


Scratching speed: V c' =76mm/s

Water lubrication

Cu

ttin

g F

orc

e (

N)



Figure 14. Scratching force varying with fiber orientation.


Materials 2018, 11, 1974 12 of 17

3.4. Scratching CFRP Composites with Diamond Indenter

In order to reveal the cutting mechanism of dicing CFRP composites, the scratching experimentsof CFRP composites with a diamond indenter were conducted on the UMT-TriboLab platform tocompare the machined quality and cutting force with different fiber orientations and indenter angles,as shown in Figure 13. Three indenters with apical angles of 60◦, 90◦, and 120◦ were chosen to reflectthe sharpness of diamond abrasive grits in the dicing blade. The sharpness of diamond indenters waswell kept before the scratching experiment. Figure 14 shows the scratching force changing with thefiber orientations and the scratching load. Under the same load force, the indenter with apical angle of60◦ generates the highest scratching force. The sharp tip allows it to indent into CFRP composites at ahigher depth. More carbon fibers take part in scratching, so the scratching force is largest. The indenterwith apical angle of 120◦ has a blunt point. It is different to indent into the CFRP. In most circumstances,it scratches on the surface of CFRP composites but does not cut the fibers. Thus, the scratching force issmall. Besides, under the large indent force, the carbon fibers often break off instead of being cut off.Moreover, fiber orientations have remarkable impact on the scratching force. As seen from the figure,the scratching force increases with the increase of fiber orientation from 0◦ to 90◦ and then goes downwith the increase of fiber orientation from 90◦ to 120◦. When scratching direction is perpendicularto fiber orientation, the scratching force is largest, which is different from the trend of dicing CFRPcomposites with the diamond blade. It indicates the two cutting actions are of different machiningmechanisms. The scratching mechanism is similar to the milling and drilling of CFRP composites.




0 30 60 90 120 150 180 210 240 270 300 330 3600

2

4

6

8

10

12

14

16

18






Water lubrication

Cutt

ing F

orc

e (

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Figure 14. Scratching force varying with fiber orientation.





0 30 60 90 120 150 180 210 240 270 300 330 3600

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Figure 14. Scratching force varying with fiber orientation. Figure 14. Scratching force varying with fiber orientation.

Materials 2018, 11, 1974 13 of 17

As shown in Figure 15, the comparisons between the morphologies of CFRP composites obtainedwith the dicing method and scratching identify that the dicing method with a diamond blade canprovide much better surface quality of CFRP composites than traditional cutting. During the dicingprocess with a diamond blade, the carbon fibers were even cut along with its axis without breakingthe carbon fibers. Only when the fiber orientation is not parallel to the dicing surface, the fibers willdebond from the matrix under the cutting force of diamond grits. Thus, there are many debondinggrooves left by carbon fibers, which is the main reason why the surface roughness is largest when thedicing direction is parallel to the fiber orientation. When the dicing direction is perpendicular to thefiber orientation as seen in Figure 15b, carbon fibers embedded well in the resin matrix are difficultto deform during the high-speed cutting process. Thus, carbon fibers are cut orderly. The surfaceroughness in this fiber direction is therefore best. In comparison with diamond blade dicing, themorphologies of CFRP composites obtained by the diamond indenter are much poorer, as presentedin Figure 15c,d. Fiber bundles debonding or breaking are the main cutting mechanisms for diamondindenter scratching. This cutting style dominates that the surface roughness of machined CFRPcomposites is larger than the scales of carbon fibers.


As shown in Figure 15, the comparisons between the morphologies of CFRP composites

obtained with the dicing method and scratching identify that the dicing method with a diamond

blade can provide much better surface quality of CFRP composites than traditional cutting. During

the dicing process with a diamond blade, the carbon fibers were even cut along with its axis without

breaking the carbon fibers. Only when the fiber orientation is not parallel to the dicing surface, the

fibers will debond from the matrix under the cutting force of diamond grits. Thus, there are many

debonding grooves left by carbon fibers, which is the main reason why the surface roughness is

largest when the dicing direction is parallel to the fiber orientation. When the dicing direction is

perpendicular to the fiber orientation as seen in Figure 15b, carbon fibers embedded well in the resin

matrix are difficult to deform during the high-speed cutting process. Thus, carbon fibers are cut

orderly. The surface roughness in this fiber direction is therefore best. In comparison with diamond

blade dicing, the morphologies of CFRP composites obtained by the diamond indenter are much

poorer, as presented in Figure 15c,d. Fiber bundles debonding or breaking are the main cutting

mechanisms for diamond indenter scratching. This cutting style dominates that the surface

roughness of machined CFRP composites is larger than the scales of carbon fibers.

Figure 15. Morphologies of CFRP composites obtained by different cutting methods.

3.5. Cutting Mechanism of CFRP Composites with Diamond Blade

According to the above analysis, the cutting mechanism of CFRP composites with a dicing blade

can be briefly concluded as illustrated in Figure 16. The cutting depth per diamond grit (about 10 nm)

during the dicing process is much smaller than the diameter of the carbon fiber (about 7 μm). Under

this machining condition, the cutting force is too small to cause the serious deformation or breaking

off of bulk fiber bundles. The cutting force of diamond grits only acts in a small region of carbon fiber

or resin matrix. Thus, serious macro damages, such as delamination, burrs, and fiber pull out, are

prevented from occurring in the dicing method, which is different from traditional machining

methods [54]. As far as fiber orientation is concerned, when the dicing direction is parallel to the fiber

orientation, fibers on the surface of CFRP composites are not embedded in matrix entirely. It is easy

for them to debond from the resin matrix under the scratching action of diamond grits. The residual

debonding grooves are the main reason in causing the increase of surface roughness. When the

cutting direction is perpendicular to the fiber orientation, carbon fibers are fixed well in the resin

matrix. Only the ends of fibers are cut by diamond grits. It is difficult for fibers to deform under the

condition of a very small cutting depth. Thus, the cutting surfaces are very smooth. Under these

Figure 15. Morphologies of CFRP composites obtained by different cutting methods.

3.5. Cutting Mechanism of CFRP Composites with Diamond Blade

According to the above analysis, the cutting mechanism of CFRP composites with a dicing bladecan be briefly concluded as illustrated in Figure 16. The cutting depth per diamond grit (about10 nm) during the dicing process is much smaller than the diameter of the carbon fiber (about 7 µm).Under this machining condition, the cutting force is too small to cause the serious deformation orbreaking off of bulk fiber bundles. The cutting force of diamond grits only acts in a small region ofcarbon fiber or resin matrix. Thus, serious macro damages, such as delamination, burrs, and fiber pullout, are prevented from occurring in the dicing method, which is different from traditional machiningmethods [54]. As far as fiber orientation is concerned, when the dicing direction is parallel to the fiberorientation, fibers on the surface of CFRP composites are not embedded in matrix entirely. It is easyfor them to debond from the resin matrix under the scratching action of diamond grits. The residualdebonding grooves are the main reason in causing the increase of surface roughness. When the cuttingdirection is perpendicular to the fiber orientation, carbon fibers are fixed well in the resin matrix.Only the ends of fibers are cut by diamond grits. It is difficult for fibers to deform under the condition

Materials 2018, 11, 1974 14 of 17

of a very small cutting depth. Thus, the cutting surfaces are very smooth. Under these circumstances,the shrinking of resin after the dicing process is the main cause in increasing the surface roughnessof machined CFRP composites due to the decrease in temperature. When the dicing direction isat an angle of 45◦ or 135◦ to the fiber orientation, the tips of fibers are easy to break off under thecutting force of diamond grits because of poor support. Thus, the surface roughness is larger thanthat of the dicing direction perpendicular to the fiber orientation. According to the study of Bifano,plastic-flow is the predominant material removal mechanism for grinding brittle materials whengrinding infeed rates are controlled as small as several nanometers per grinding wheel revolution [55].Although somewhat brittle, the cross-section surface of carbon fiber finishes similar to those achievedin polishing or lapping, are achieved in this high-speed dicing process due to the plastic-flow materialremoval mechanism.


circumstances, the shrinking of resin after the dicing process is the main cause in increasing the

surface roughness of machined CFRP composites due to the decrease in temperature. When the

dicing direction is at an angle of 45° or 135° to the fiber orientation, the tips of fibers are easy to break

off under the cutting force of diamond grits because of poor support. Thus, the surface roughness is

larger than that of the dicing direction perpendicular to the fiber orientation. According to the study

of Bifano, plastic-flow is the predominant material removal mechanism for grinding brittle materials

when grinding infeed rates are controlled as small as several nanometers per grinding wheel

revolution [55]. Although somewhat brittle, the cross-section surface of carbon fiber finishes similar

to those achieved in polishing or lapping, are achieved in this high-speed dicing process due to the

plastic-flow material removal mechanism.

Figure 16. Schematic diagram of dicing mechanism with different fiber orientations.

4. Conclusions

This study presented the benchmarking investigation and analysis of high-speed low-damage

micro-cutting of CFRP composites with diamond abrasive blades, particularly in light of obtaining

nanoscale smooth surfaces of CFRP composites by introducing nanoscale cutting depth of diamond

grits. The paper also presented the dicing mechanism in high-speed micro-cutting of CFRP

composites. The surface morphology of the processed specimens with different rotational speeds and

fiber orientations were further studied to evaluate and validate the mechanism and analysis. The

concluding results are summarized as follows:

(1) Dicing with diamond abrasive blades enables machining CFRP composites with a high

cutting speed of more than 76 m/s (25,000 rpm). The high cutting speed not only remarkably increases

the rigidity of the ultra-thin dicing blade, but also decreases the cutting depth per diamond grit to

below 10 nm. Both result in a fine surface finish of machined CFRP composites. However, the serious

vibration of the spindle in the horizontal direction limits the rotational speed to increase further. Best

machined surface quality occurs at the rotational speed of 25,000 rpm. The surface roughness of

machined CFRP composites have a similar tendency as the cutting current of the machine mainly due

to the spindle vibration having a more important influence on the cutting current than the cutting

force. Thus, it is necessary to reduce the vibration when the rotational speed is more than 25,000 rpm.

(2) The cutting currents of the spindle motor present an overall V-shape tendency when the fiber

orientation angle changes from 0° to 180° due to the mechanical anisotropy of CFRP composites. The

maximum value occurs at the fiber orientation of 0°, while the minimum value occurs at the fiber

orientation of 90°. With the fiber orientation changing from 0° to 90°, the cutting current presents an

overall decrease but a slight increase at about 40°. This tendency is different from most reported

research about the milling and drilling of CFRP composites. It may be attributed to the different

cutting mechanism of the dicing method with drilling and milling methods. The surface roughness

of machined CFRP composites has a similar tendency with the cutting current. When the cutting

direction is perpendicular to the fiber orientation, the machined CFRP composite obtains the best

surface finish at about Ra 0.025 μm, which is lower than most reported results. Furthermore, the

metal-bonded dicing blade achieves smaller surface roughness than the resin-bonded dicing blade

Figure 16. Schematic diagram of dicing mechanism with different fiber orientations.

4. Conclusions

This study presented the benchmarking investigation and analysis of high-speed low-damagemicro-cutting of CFRP composites with diamond abrasive blades, particularly in light of obtainingnanoscale smooth surfaces of CFRP composites by introducing nanoscale cutting depth of diamondgrits. The paper also presented the dicing mechanism in high-speed micro-cutting of CFRP composites.The surface morphology of the processed specimens with different rotational speeds and fiberorientations were further studied to evaluate and validate the mechanism and analysis. The concludingresults are summarized as follows:

(1) Dicing with diamond abrasive blades enables machining CFRP composites with a high cuttingspeed of more than 76 m/s (25,000 rpm). The high cutting speed not only remarkably increasesthe rigidity of the ultra-thin dicing blade, but also decreases the cutting depth per diamond grit tobelow 10 nm. Both result in a fine surface finish of machined CFRP composites. However, the seriousvibration of the spindle in the horizontal direction limits the rotational speed to increase further.Best machined surface quality occurs at the rotational speed of 25,000 rpm. The surface roughnessof machined CFRP composites have a similar tendency as the cutting current of the machine mainlydue to the spindle vibration having a more important influence on the cutting current than the cuttingforce. Thus, it is necessary to reduce the vibration when the rotational speed is more than 25,000 rpm.

(2) The cutting currents of the spindle motor present an overall V-shape tendency when the fiberorientation angle changes from 0◦ to 180◦ due to the mechanical anisotropy of CFRP composites.The maximum value occurs at the fiber orientation of 0◦, while the minimum value occurs at the fiberorientation of 90◦. With the fiber orientation changing from 0◦ to 90◦, the cutting current presentsan overall decrease but a slight increase at about 40◦. This tendency is different from most reportedresearch about the milling and drilling of CFRP composites. It may be attributed to the differentcutting mechanism of the dicing method with drilling and milling methods. The surface roughness ofmachined CFRP composites has a similar tendency with the cutting current. When the cutting directionis perpendicular to the fiber orientation, the machined CFRP composite obtains the best surface finish

Materials 2018, 11, 1974 15 of 17

at about Ra 0.025 µm, which is lower than most reported results. Furthermore, the metal-bondeddicing blade achieves smaller surface roughness than the resin-bonded dicing blade when cutting withall fiber orientations due to its good thermal conductivity and low friction coefficient.

(3) In comparison with scratching CFRP composites with the diamond indenter, the mechanismof high machining quality achieved with the dicing blade is mainly attributed to the nanoscale cuttingdepth of diamond grits. Such a thin cutting layer allows the material removal to only occur at localregions of carbon fiber or resin matrix. The high cutting speed and low cutting force prevent seriousdeformation or breaking off of bulk fiber. The micro breakage and plastic-flow in local regions are themain material removal mechanisms for dicing CFRP composites with diamond abrasive blades. Thus,the surface roughness of machined CFRP composites mainly depends on the styles of micro breakage.When cutting in the direction perpendicular to the fiber orientation, the surface roughness is lowestdue to the well fixation of fibers in resin matrix. However, when cutting in the direction parallel to thefiber orientation, the debonding of fibers causes relative poor machining quality.

Author Contributions: Conceptualization, Z.Y. and J.H.; methodology, Z.Y. and Q.W.; validation, Z.Y., K.C. andP.Z.; formal analysis, J.H. and Q.W.; investigation, Z.Y. and J.H.; resources, Z.Y.; data curation, J. Hu and Q.W.;writing—original draft preparation, Z.Y.; writing—review and editing, K.C. and P.Z.; supervision, K.C.; projectadministration, Z.Y.; funding acquisition, Z.Y.

Funding: This research was funded by the National Science Foundation of China (Grant No. 51305278; GrantNo. 51505074), the Basic Research Foundation of Liaoning Province Universities (Grant No. LFGD2017007),the Natural Science Foundation of Shenyang City (Grant No. F16-205-1-10), the China Postdoctoral ScienceFoundation (Grant No. 2014M551124) and the Program of China Scholarships Council (Grant No.201708210034).

Acknowledgments: The authors would like to thank Shenyang Changpu Superhard Precision Tools Co.LTD for providing the dicing blades and Brunel University London for hosting the academic visit andresearch collaboration.

Conflicts of Interest: The authors declare no potential conflicts of interest with respect to the research. Thefunders had no role in the design of the study; in the collection, analyses, or interpretation of data; in the writingof the manuscript, or in the decision to publish the results.

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